1. Field of the Invention
The invention relates to a method for producing a semiconductor wafer with a profiled edge, in which the semiconductor wafer is separated from a crystal and subjected to further machining steps.
2. Background Art
The invention relates, in particular, to a method for producing a semiconductor wafer which serves as a substrate wafer for electronic circuits, for example a semiconductor wafer composed of silicon or a compound semiconductor or else a semiconductor wafer which is constructed in layered fashion and comprises at least one layer composed of semiconductor material. The production of such semiconductor wafers constitutes a particular challenge since they have to meet extremely stringent requirements not only with regard to the purity of the material used but also with regard to form and flatness.
Customary machining steps devoted to shaping the semiconductor wafer after separation from a crystal aim to give the semiconductor wafer a form which is distinguished, in particular, by a profiled edge and sides that are opposite one another in plane-parallel fashion. A machining step that produces an edge profile is necessary because the edge is particularly susceptible to breaking in the non-machined state and a semiconductor wafer can be damaged even by slight pressure and/or temperature loadings in the edge region. The shaping machining steps include, besides an edge profile producing step, in particular lapping and grinding of the sides. The two mechanical machining steps mentioned last can be employed together, lapping followed by grinding, or in such a way that only one of the two machining steps is performed. The grinding of the side can be subdivided into rough and fine grinding steps depending on the grit of the abrasive grain used. Furthermore, the grinding may be restricted to one side of the semiconductor wafer or encompass both sides of the semiconductor wafer. If both sides are to be ground, then this can be carried out successively or in one step. DE 10 2004 005 702 A1 describes a double-side grinding machine having double spindles and a method carried out with this machine in which both sides of a semiconductor wafer are ground simultaneously. The semiconductor wafer is guided in a free-floating and rotating fashion between two mutually opposite grinding discs and is held in position by a guide ring (rotor ring) surrounding it. The rotary movement of the semiconductor wafer is brought about for example by a notch finger, which engages in an orientation notch on the circumference of the semiconductor wafer, or by a friction belt which partly encloses the semiconductor wafer on the circumference. A prerequisite for the undisturbed rotary movement is that the semiconductor wafer is round, that is to say has a circular circumference.
Semiconductor wafers in which the orientation of the crystal lattice deviates slightly from the orientation of the crystal from which they were separated have advantageous properties which become apparent particularly in thermal treatments and methods in which layers are deposited on the semiconductor wafer. In accordance with DE 199 54 349 A1, semiconductor wafers with misorientation are obtained if the semiconductor wafers are not separated perpendicular to the crystal axis, but rather at an angle that deviates therefrom and corresponds to that of the intended misorientation. Elliptically shaped semiconductor wafers are obtained from a crystal having a uniform diameter ground in round fashion. Owing to this shape, such a semiconductor wafer initially cannot be subjected to a mechanical machining of the sides by simultaneous grinding of the sides. A comparatively complicated possibility for avoiding this problem consists, for example, in separating the misoriented semiconductor wafers from a crystal having an elliptical cross-sectional area which is dimensioned in such a way that round semiconductor wafers arise during separation.
The machining step that produces an edge profile may be effected before or after the mechanical machining of the sides of the semiconductor wafer. What is disadvantageous with regard to a machining step that does not produce the edge profile until after the sides of the semiconductor wafer have been mechanically machined is that the edge is so sensitive in the unmachined state that the semiconductor wafer often does not withstand the mechanical machining of the sides without being damaged in the process. A semiconductor wafer with a profiled edge still remains sensitive, however, even though serious damage such as edge chips and cracks is less common. Therefore, it is likewise disadvantageous if the edge profile is produced before the mechanical machining takes place, because later damage to the edge can no longer be completely repaired.
U.S. Pat. No. 6,066,565 describes a method in which the edge profile is produced in two separate mechanical machining steps, between which the mechanical machining of the sides of the semiconductor wafer is provided. In the first of the two steps, the edge is chamfered at the sides, part of the edge remaining unmachined. The aim of this method is to stabilize the edge by means of the first rough machining such that serious damage is avoided in the subsequent side grinding step, which aims to retain the symmetry of the semiconductor wafer with regard to a horizontal reflection plane. What is disadvantageous about this method is that the edge of the semiconductor wafer has, during the mechanical machining of the sides, a region that has not yet been machined and is therefore particularly sensitive, and, as a result, is not protected much better than if the edge machining had not taken place at all.